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Fair Value Measurements (Narrative) (Detail) - USD ($) | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Virginia Electric and Power Company |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Unrealized gains or losses included in earnings in Level 3 fair value category | $ 0 | $ 0 | $ 0 | $ 0
Dominion Energy Gas Holdings, LLC |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Unrealized gains or losses included in earnings in Level 3 fair value category | 0 | 0 | $ 0 | $ 0
Dominion Energy Gas Holdings, LLC | Commodity contracts |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Net changes in assets and liabilities measured at fair value on recurring basis | $ 0 | $ 0 |  |

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- Definition Amount of realized and unrealized gain (loss) included in earnings, which have arisen from the use of significant unobservable inputs (level 3) to measure fair value of assets, liabilities, and financial instruments classified in shareholders' equity. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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